def resolve():
    import math
    x1, y1, x2, y2 = [float(i) for i in input().split()]
    print(math.sqrt((x2 - x1)**2 + (y2 - y1)**2))


resolve()
 def resolve():
    import math
    x1, y1, x2, y2 = [float(i) for i in input().split()]
    print(math.sqrt((x2 - x1)**2 + (y2 - y1)**2)) resolve import math math float(i) for i in input().split() for i in input().split() i input().split() ().split () input split for i in input().split() float(i) float i x1, y1, x2, y2 = [float(i) for i in input().split()] x1 [float(i) for i in input().split()] y1 x2 y2 print(math.sqrt((x2 - x1)**2 + (y2 - y1)**2)) print math.sqrt((x2 - x1)**2 + (y2 - y1)**2) math.sqrt math sqrt (x2 - x1)**2 + (y2 - y1)**2 (x2 - x1)**2 x2 - x1 x2 x1 2 (y2 - y1)**2 y2 - y1 y2 y1 2 resolve() resolve def resolve():
    import math
    x1, y1, x2, y2 = [float(i) for i in input().split()]
    print(math.sqrt((x2 - x1)**2 + (y2 - y1)**2)) def resolve():
    import math
    x1, y1, x2, y2 = [float(i) for i in input().split()]
    print(math.sqrt((x2 - x1)**2 + (y2 - y1)**2)) resolve
def resolve():
    import math
    x1, y1, x2, y2 = [float(i) for i in input().split()]
    print(math.sqrt((x2 - x1)**2 + (y2 - y1)**2))


resolve()

